1. Field of the Invention
The present invention relates to an objective soft focus lens system for use in photography and more particularly to an improved soft focus lens system that eliminates undesirable aberrations.
2. Brief Description of the Prior Art
Soft focus lens system have been used in the photography field for a considerable period of time. Various different soft focus lens systems have been suggested such as those disclosed in U.S. Pat. No. 2,233,591; U.S. Pat. No. 1,370,885; U.S. Pat. No. 3,843,235; U.S. Pat. No. 3,397,023; U.S. Pat. No. 3,045,530; U.S. Pat. No. 2,959,105 and U.S. Pat. No. 3,476,457. Various apodization optical systems have also been described for achieving a blurred or soft focus image of a target photographing object. Frequently, soft focus filters have been suggested which are permanently mounted in a lens barrel, traversely removable from the lens barrel or attached to the end of the lens barrel.
One of the known ways of designing a soft focus lens system is to intentionally increase the amount of spherical aberration beyond the normal tolerance limits. By varying the spherical aberration introduced into the image an adjustable soft focus lens system can be achieved and such a system is disclosed in British Pat. No. 198,569 published June 7, 1923. The object of the British patent reference was to provide a soft focus objective and high speed anastigmatic combination lens system. This was accomplished by providing at least two sets of lenses wherein one lens was adjusted relative to the other lens set for the purpose of changing the lens from an anastigmatic to a soft lens.
The prior art has experienced difficulties in achieving a satisfactory commercial soft focus lens system that can be economically produced free from undesirable aberrations. These undesirable aberrations are usually introduced into the lens system by any variation in the introduction of spherical aberration. Frequently, the focus of the lens of the total lens system is usually not maintained during the variation of the spherical aberration and the operator has to re-adjust the focusing of the total lens system when the spherical aberration is varied. As can be readily appreciated the adjustment of the focus of the total lens system can be difficult when viewing a soft tone image through the viewfinder.
The prior art has not suggested an improved soft focus lens system that is capable of providing a highly desirable portrait image with a minimum of aberrations.